Following graduation, Wertheim worked as a volunteer research assistant at the Institute of Pacific Relations in New York, spending a year in Tokyo in 1934-35, including a month in China, before returning to the United States via the Trans-Siberian Railway to Moscow and on to Paris.[2] She also contributed to The Nation as a correspondent until her father's sale of the publication in 1937, traveling to Valencia and Madrid to cover the Spanish Civil War.[4] A first book resulted from her Spanish experience, The Lost British Policy: Britain and Spain Since 1700, published in 1938.

During the years of World War II, Tuchman worked in the Office of War Information.[2] Following the war, Tuchman spent the next decade working to raise the children while doing basic research for what would ultimately become the 1956 book Bible and Sword: England and Palestine from the Bronze Age to Balfour.[2]

With the publication of Bible and Sword in 1956, Tuchman dedicated herself to historical research and writing, turning out a new book approximately every four years.[2] Rather than feeling hampered by the lack of an advanced degree in history, Tuchman argued that freedom from the rigors and expectations of academia was actually liberating, as the norms of academic writing would have "stifled any writing capacity."[2]

Tuchman favored a literary approach to the writing of history, providing eloquent explanatory narratives rather than concentration upon discovery and publication of fresh archival sources. In the words of one biographer, Tuchman was "not a historian's historian; she was a layperson's historian who made the past interesting to millions of readers."[6] Tuchman's storytelling prowess was rewarded in 1963 when she received the Pulitzer Prize for her book The Guns of August, dealing with the behind-the-scenes political machinations which led to the eruption of World War I in the summer of 1914.

In the introduction to her 1978 book A Distant Mirror, Tuchman playfully identified a historical phenomenon which she termed "Tuchman's Law," to wit:

Disaster is rarely as pervasive as it seems from recorded accounts. The fact of being on the record makes it appear continuous and ubiquitous whereas it is more likely to have been sporadic both in time and place. Besides, persistence of the normal is usually greater than the effect of the disturbance, as we know from our own times. After absorbing the news of today, one expects to face a world consisting entirely of strikes, crimes, power failures, broken water mains, stalled trains, school shutdowns, muggers, drug addicts, neo-Nazis, and rapists. The fact is that one can come home in the evening — on a lucky day — without having encountered more than one or two of these phenomena. This has led me to formulate Tuchman's Law, as follows: "The fact of being reported multiplies the apparent extent of any deplorable development by five- to tenfold" (or any figure the reader would care to supply).[14]

Tuchman's Law has been defined as a psychological principle of "perceptual readiness" or "subjective probability".[15]

America's Security in the 1980s. London: International Institute for Strategic Studies, 1982.

The Book: A Lecture Sponsored by the Center for the Book in the Library of Congress and the Authors’ League of America, Presented at the Library of Congress, October 17, 1979. Washington, DC: Library of Congress, 1980.